Making Up for Temporal Slack

The sun follows its own clock

By J. Alex Knoll

As darkness falls, first Venus then Jupiter pop into view in the wake of the setting sun. Venus blazes at magnitude –4.4, exponentially brighter than Jupiter at magnitude –2, which still outshines any star. The two planets are inching closer on their way to an end-of-month rendezvous. This week the gap between the two shrinks to 10 degrees — close enough to obscure both with your fist held at arm’s length.
Keep an eye on Venus this weekend. It is near the center of the dim Y-shaped constellation Cancer, which in itself is not that interesting, boasting no star brighter than 3.5 magnitude. In fact, were it not placed on the ecliptic, the path of the sun, moon and planets as they circle overhead, Cancer would be a minor constellation, certainly not a denizen of the zodiac or even an astrological sign. Cancer’s claim to fame is no star but what appears as a faint, fuzzy patch of light to the unaided eye, M44, the Beehive Cluster.
Viewed with binoculars, however, the Beehive comes to life with dozens of stars, and with a telescope it swarms with hundreds of stars. Friday and Saturday Venus is less than one degree from the Beehive in the western sky at nightfall and visible for at least an hour after sunset.
Friday marks our earliest sunrise of the year, almost 10 days before the solstice. The discrepancy is the result of several factors, but in short, our clocks keep different time than the sun. While the clock measures a day with the passing of each 24 hours, a solar day is measured from the time of one high noon to the next. Hereabouts on the 12th, that is 24 hours and 15 seconds. Prior to the solstice this temporal slack is made up for at dawn, while after solstice the difference is at sunset. So while the summer solstice is June 21, our earliest sunrise is always some 10 days before, and the latest sunset another 10 days after solstice. In winter, the same phenomenon is at play, only reversed, and more pronounced, with nearly two weeks between earliest sunset and solstice and solstice and latest sunrise.